Reinforced flexible abrasive wheel



Aug. 2, 1966 v. K. CHARVAT REINFORCED FLEXIBLE ABRASIVE WHEEL Filed Dec.15, 1963 Ill/Ill ATTORNEYS United States Patent 3,263,377 REINFORCEDFLEXIBLE ABRASIVE WHEEL Vernon K. Charvat, Bay Village, Ohio, assignorto The Osborn Manufacturing Company, Cleveland, Ohio, a corporation ofOhio Filed Dec. 13, 1963, Ser. No. 330,347 13 Claims. (Cl. 51-394) Thepresent invention relates in general to abrasive wheels and moreparticularly, as indicated, to a reinforced flexible abrasive wheel.Such a flexible type abrasive wheel finds use, for example, in finishingand/ or polishing workpieces, the flexibility thereof permitting theface of the wheel to follow closely the surface of the workpiece therebyto provide the desired polishing or finishing operation withoutsubstantial cutting of the workpiece, which distinguishes such flexiblewheels from the relatively rigid grinding type wheels which are able tomake relatively deep cuts in the workpiece.

In flexible abrasive wheels, there are certain desired characteristicswhich such wheels should possess to provide optimum results overextended periods of frequently high speed use. The wheel must of coursebe flexible, which places a decided limitation on the material formingthe matrix or body of the abrasive wheel. Secondly, the wheel, whilepossessing the requisite flexibility, should during continued periods ofuse retain its concentricity with the arbor. In this regard, there is astrong tendency, especially during relatively high speed rotation, forthe materials which form the wheel to expand or stretch radiallyoutwardly, usually in a non-uniform manner, thereby to effect anon-smooth working surface, an obviously undesirable result. Such radialstretching also tends to increase the arbor hole size resulting inundesirable eccentric rotation.

A primary object of the present invention, then, is to provide aflexible abrasive wheel possessing the desired flexibility but which isresistant to radially outward expansion even during relatively highspeed use so as to retain peripheral concentricity with the arbor.

A more specific object of the present invention is to provide aninternally reinforced flexible abrasive wheel constructed to permityielding where necessary and desired but wherein such reinforcingrigidifies the wheel for retaining its shape and concentricity evenduring high speed use and under relatively heavy loads. In other words,such reinforcing means permits substantial movement of the face of thewheel for following closely the surface of the workpiece but yetprovides radial rigidity to the wheel for retaining the shape thereof.

A further object of the present invention is to provide such an internalreinforcing means for imparting to the wheel the noted resistance toradial expansion, but which itself is relatively lightweight andlaterally flexible so as not to impair the lateral flexibility of theflexible wheel to any significant degree.

A still further object of the present invention is to provide afinishing and polishing wheel of foamed flexible plastic having granularabrasive concentrated only in a radially outer annular region thereofwhich, together with the comparatively lightweight internal reinforcingmeans, comprises a flexible abrasive wheel of substantially less weightthan existing wheels of this general type.

A still further object of the present invention is to provide a novelmethod of making the flexible abrasive wheel with the reinforcing meansincorporated therein.

These and other objects and advantages of the present invention willbecome apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawings setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principle of the invention may beemployed.

In said annexed drawings:

FIG. 1 is a side elevational view of the abrasive wheel of the presentinvention, incorporating one form of the flexible reinforcement, withthe abrasive wheel being broken away in the central portion thereof toexpose such reinforcing member;

FIG. 2 is a radial sectional view taken on lines. 2-2 of FIG. 1, withcertain material along the section line being omitted to expose thereinforcing member;

FIG. 3 is a side elevational view of an abrasive wheel incorporating asecond form of reinforcing member and means for axially spacing the samewithin the mold, with the central portion of such wheel being brokenaway to expose such reinforcing member;

FIG. 4 is a radial sectional view taken on lines 4-4 of FIG. 3, withcertain material along the section line being omited to expose thereinforcing member;

FIG. 5 is a fragmentary view showing another means for spacing thereinforcing member of the FIGS. 3-4 form within the mold; and

FIG. 6 is a partially sectioned side view of the preferred moldapparatus for molding the reinforced flexible abrasive wheel of thepresent invention, with the mold parts being shown disassembled.

Referring now in more detail to the drawings, wherein like referencecharacters are used to designate like parts, and initially to FIGS. 1and 2 thereof, the flexible abrasive wheel illustrated in completed formtherein is generally indicated at 10 and comprises a body portion 12 ofrelatively low density foamed plastic having abrasive particles embeddedtherein in a radially outer annular belt or region relatively adjacentthe periphery or working surface of the wheel. Although the particularcomposition of the foamed plastic body 12 forms no part of the presentinvention, with any suitable plastic mixture possessing the suitablefoaming properties and being elasto-meric upon setting being capable ofuse, highly satisfactory results have been obtained where the foamedplastic comprises polyurethane. Generally stated, such polyurethane foamcomprises a gellable, foamable liquid resin and is combined with certainother ingredients such as, e.g., relatively inert or neutral fillingmaterial, catalysts, water, and of course the abrasive particles. Theamount of the entire mixture is less than the mold cavity so as to allowfor foaming and the incidental generation of gas bubbles during themolding process to be hereinafter specifically described. Substantiallyall of the abrasive particles or granules 14 during such molding processwill move toward the radially outer regions of the wheel to form anouter annular abrasive region adjacent the periphery thereof. Theparticular plastic employed, the flexibility thereof, and the type ofabrasive particles embedded therein will depend upon the particular useto which the wheel is put. It will be understood that the elastomericplastic foam employed should have the desired degree of softness, i.e.,flexibility sufiicient to do effectively the work intended.

Referring now in more detail to the means for reinforcing the wheel 10,a centrally disposed reinforcing member or skeleton 16 is embeddedwithin the relatively non-abrasive region of the foam plastic body 12during the molding of the wheel, the skeleton 16 being preferablyconstructed of a relatively lightweight laminated fibrous compositionsuch as, e.g., cardboard. Such fibrous composition, and moreparticularly the configuration thereof, permits lateral deflection ofthe skeleton but resists radial expansion thereby to maintain thedesired concentricity of the abrasive wheel. As can readily be seen inFIG. 2, the skeleton 16 is relatively thin in comparison with the totalthickness of the abrasive wheel 10. Such thinness, in addition toproviding the desired lateral flexibility, is desirable during themolding of the wheel 10, as will be hereinafter explained.

Referring to the specific configuration of the skeleton- 16 in the FIGS.1-2 form thereof, the skeleton 16 comprises a central body portion 18formed with an opening 20 which defines the arbor opening for thefinished wheel. A plurality of arcuately spaced openings 22 are formedin such central portion 18 of the skeleton for a reason hereinafterexplained. Such central portion further includes a plurality ofarcuately spaced tabs 24 and 26 upset from the central body portion andwhich extend normally thereto on both sides thereof. There are thus inthe form shown four such tabs 24 which extend to one side of theskeleton and a second set of tabs 26 radially spaced outwardly from thetabs 24 and which extend in the opposite direction relative thereto. Theoppositely directed tabs 24 and 26 serve to accurately axially set theskeleton 16 in the mold during the molding process thereby to ensureaxial centering thereof in the completed Wheel.

The skeleton 16 is further formed with a plurality of radial,finger-like extensions 28, each of which is generally triangular shapedwith a relatively large opening therein and connected to the centralbody portion through neck portions 30. The width of the neck portions 30should be relatively small, for example approximately twice thethickness of the skeleton, to permit the desired lateral movement ortwisting of the skeleton in use of the wheel. The arcuate length alongthe outer periphery of each of the extensions 28 is likewise ofimportance in controlling the twisting action of the wheel since thefoam plastic material rigidly chemically bonded thereto yields intension as the wheel is laterally flexed, with the resistance affordedby the bonded interface varying with the length of the arcuate peripheryof the extension.

In addition to controlling the lateral deflection of the skeleton 16,the arcuately spaced extensions 28, and more particularly the open areas32 therebetween, serve effectively to key mechanically the foamedplastic to the skeleton 16. Thus, during the molding process, the foamedplastic enters such open areas 32 between the extensions 28, as well asthe openings 22 in the central portion 18 of the skeleton, therebymechanically keying the skeleton 16 to the plastic. As will beunderstood, in addition to such mechanical keying of the skeleton to thefoam plastic, a rigid chemical bonding between the plastic and thesurface of the skeleton will be effected. The open areas of the skeleton16 in the form shown comprise approximately 50 percent of the total areaof the skeleton.

Referring now to the abrasive wheel illustrated in FIGS. 3 and 4, withone exception the reinforcing skeleton illustrated therein is identicalwith that previously described above in reference to the FIGS. 1 and 2embodiment, such similarity where present being indicated by the use oflike reference characters. In FIGS. 3 and 4 form, however, the tabs 24and 26 have been omitted and the'skeleton 16 is completely flat. Inorder accurately to space the skeleton 16 within the mold during themold ing process, a plurality of arcuately spaced openings 34 are formedin the central body portion 18 of the skeleton, and pins 36 are disposedtherethrough, the opposed flat ends of such pins extending equaldistances from each side of the skeleton so as accurately to space theskeleton within the mold. Although it will be apparent that theparticular material employed for such pins is not critical, suchmaterial should be preferably capable of deformation rather thanbreakage in order to absorb forces acting thereon when the wheel ismounted for use, and in this regard polypropylene has been found to bean excellent material for this purpose. In addition to spacing theskeleton 16 within the mold, when the wheel 10 is mounted tightly withinarbor assembly, the opposed ends of the pins 36 are generally contactedby the arbor mounting flanges to thus provide relatively rigid points ofcontact therebetween which tend greatly to decrease slippage of thewheel under the torque resulting from the pressure of the work.

There is illustrated in FIG. 5 yet another means for spacing theskeleton 16 within the mold during the molding process. In this form, aplurality of pins, one such pin being indicated at 36', are similarlyused for such spacing. However, rather than being of the straight formshown in FIG. 4, the pins in the FIG. 5 form are provided with headportions 38, the depth of such head portions being predeterminedlycalculated to ensure proper location of the skeleton within the mold.The opposite end of the pin 36' extends outwardly from the opposite faceof the skeleton 16 an amount equal to the depth of the head 38 wherebythe skeleton is accurately axially aligned in the mold when disposedtherein.

There is diagrammatically shown in FIG. 6 suitable molding equipment formolding the wheel 10 in accordance with the present invention, and themethod of centrifugal molding is preferably employed. The centrifugalmolding process by itself forms no part of the present invention andwill be described only in sufficient detail to enable one skilled in theart to fully understand the present invention and more particularly thepreferred process by which the wheel 10 is formed. For a more completediscussion of the various methods of and apparatus for making articlesby the centrifugal molding process, attention is hereby directed to myco-pending applications Serial No. 854,468, filed November 20, 1959, andSerial No. 15,135, filed March 15, 1960.

, Referring now to FIG. 6, the mold comprises an annular ring 40 adaptedto be centered and firmly secured to or clamped against a bottom plate42 preferably detachably secured to a turntable support 44. The support44 is rotatable about a vertical axis by any suitable drive means, forexample a motor 46 and a worm gear assembly, the latter being enclosedin housing 48. As will be apparent, annular rings 40 having varyingdiameters may be employed to form various sized flexible abrasivewheels.

The mold further includes a removable cover plate 50 having a centralopening 52 adapted to fit over an axially threaded stud 54 whereby suchcoverplate 50 may be firmly clamped against ring 40 upon tightening of afastening nut 56. The foamable plastic ingredients and abrasive may beadded simultaneously to the mold with the cover 50, of course, removedtherefrom, in which event the cover 50 may be imperforate as shown. If,however, it is desired to add one or more of such ingredients after theplate 50 has been securely clamped in place and mold rotation initiated,the plate 50 may be additionally provided with an opening through whichsuch ingredients can be added to the mold interior, with the openingpreferably being closed during centrifuging. Sufficient clearance -orother vent means is provided centrally of cover 50 to permit escape ofexcess gas generated during the foaming and centrifuging operations.

Regardless of the manner in which the ingredients which form the foamedplastic are added to the mold, the skeleton 16 is placed within the moldwith the arbor opening 20 fitting around the stud 54. The skeleton 16 isaxially aligned within the mold by the various previously describedspacing means, namely by tabs 24-26, pins 36, or pins 36. Subsequent tothe addition of the desired plastic ingredients, the mold is rapidlyrotated, causing the abrasive particles 14 to collect, by centrifugalforce, in an annular region in the outer portion of the mold cavity, asclearly illustrated in FIGS. 2 and 4. The foaming tendency is normallyinhibited during centrifuging while the viscosity of the plasticincreases, so that upon cessation of effective centrifuging the foamingtake place in the more viscous plastic to space the abrasive granulesonly slightly but uniformly apart and completely fill the mold cavity byradially inward expansion. Such foaming action is attended by an excessof gas, and such gas is allowed to escape from the mold interior by theaforesaid central venting means. The foamed plastic material thuscompletely fills the openings 32 between the extensions 28 of theskeleton, the openings within the extensions 28, and the openings 22 inthe central portion 18 of the skeleton, the relative thinness of theskeleton 16 freely permitting flow of the plastic foam in the centralregion of the mold.

At the termination of the centrifuging operation, the plastic mixture isleft in the mold for a period of time suflicient to cure the same, withor without the addition of heat. The skeleton 16 is thereby effectivelymechanically keyed and firmly adhesively bonded to the foamed plastic.After such curing, the completed wheel is removed from the mold.

It will thus be seen that the flexible abrasive wheel made in accordancewith the present invention is unique and possesses distinct advantagesover previously known flexible type abrasive wheels. The centrifugingoperation employed permits the abrasive particles to be concentrated ina relatively narrow annular region band adjacent the periphery of thewheel. The Wheel 10, although freely flexible in the outer regionsthereof and laterally flexible throughout its entire radial dimension,is rigidly reinforced by the skeleton 16 which substantially entirelyprevents radial expansion of the wheel even at relatively high speedusesthereof. In fact, the wheel 10 has been run at speeds in excess of 1750r.p.m. under heavy loads, with no measurable loss of concentricity. Theskeleton in addition serves to flx the arbor hole size and thuseliminates the problem of eccentric rotation or the necessity of havingthe foam plastic material itself rigid enough to hold such arbor size.In previous flexible abrasive wheels having no such reinforcement means,the making of the foamed plastic rigid enough to hold the arbor size wasattended by a sacrifice of lateral flexibility thereby impairingpolishing or finishing in use of the wheel. Through use of the skeletonreinforcement of the present invention, a flexible abrasive wheel can bedesigned having in mind the optimum characteristics for polishing orfinishing without regard to previously required considerations such as,e.g., radial expansion and ability of the wheel to hold the arbor size.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

I therefore particularly point out and distinctly claim as my invention:

1. A finishing and polishing wheel comprising a body of foamed flexibleplastic having granular abrasive concentrated in an outer annular regionthereof, a flexible reinforcing skeleton embedded within the inner,relatively non-abrasive region of said plastic body, said skeleton beingradially rigid thereby to prevent substantial radially outward expansionof said body when the wheel is rotated at high speed in use, but saidskeleton being laterally flexible to permit an appreciable degree oflateral deformation of the working face of the tool in use.

2. A finishing and polishing wheel comprising a body of foamed flexibleplastic having granular abrasive concentrated in an outer annular regionthereof, a flexible rein-forcing skeleton incorporated within the inner,relatively non abrasive region of said body, said skeleton beingrelatively rigid radially to prevent substantial radially outwardexpansion of said body when the wheel is rotated at high speed in use,but said skeleton being laterally flexible to permit an appreciabledegree of lateral deformation of the Working face of the wheel in use,said skeleton being relatively thin when compared to the thickness ofsaid wheel and being provided with means for axially centering saidskeleton in said wheel.

3. The combination of.cl=aim 2 wherein said centering means comprises aplurality of integral tab members upset from a central body portion ofsaid skeleton and directed to both sides thereof substantially normalthereto, the terminal portions of said tabs at both sides of saidcentral body portion extending therefrom equidistantly.

4. The combination of claim 2 wherein said spacing means comprises aplurality of pins extending through openings in a central body portionthereof, the ends of each of said pins being equidistant from the sidesof said central body portion.

5. The combination of claim 4 wherein at least certain of said pins areformed with head portions for achieving such equidistant spacing uponinsertion of said pins in said openings.

6. In a method of molding an annular flexible body of foam plastic in acircular mold rotatable about a substantially vertical axis, the stepswhich comprise placing a radially rigid and laterally flexiblereinforcing member within said mold in a manner to axially center thesame within the mold, confining a plastic liquid body within saidcircular mold, rapidly rotating said mold, foaming such plastic body tocause the same to expand thereby filling the entire mold cavity and thussurrounding said reinforcing member, and setting such plastic therebyfirmly to embed said reinforcing member Within said plastic.

7. In a method of molding an annular flexible body of foamed plastic ina circular mold rotatable about a substantially vertical axis, the stepswhich comprise axially centering a radially rigid and laterally flexiblereinforcing skeleton within said mold concentric with the vertical axisthereof, confining a plastic liquid body having abrasive particlesassociated therewith in said mold, rapidly rotating said mold about saidvertical axis thereby to distribute said abrasive particles in aconcentrated, radially outer annular region, foaming such plastic bodyto cause the same to expand thereby filling said mold cavity andsurrounding said skeleton, and setting such plastic thereby to firmlyembed said skeleton within said plastic.

8. A finishing and polishing wheel comprising a body of flexible resin,granular abrasive within said body, a flexible reinforcing skeleton oflaminated fibrous composition embedded within said body, said skeletonbeing relatively rigid in a radial direction but laterally flexiblethereby to prevent substantial radially outward expansion of said bodybut to permit an appreciable degree of lateral deformation of theWorking .face of the wheel in use.

9. An abrasive wheel comprising a flexible body, granular abrasivewithin said body, a flexible reinforcing skeleton of laminated fibrouscomposition embedded within said body, the skeleton being relativelyrigid in a radial direction but laterally flexible thereby to preventsubstantial radially outward expansion of said body but to permit anappreciable degree of lateral deformation of the working face of thewheel in use.

10. A finishing and polishing wheel having a resin and abrasive bodynormally laterally flexible under lateral pressures encountered in useand radiaitly distensible under centrifugal force at operating speedsencountered in use, a flexible reinforcing skeleton embedded within saidbody and concentric therewith, said skeleton extending radiallyoutwardly from the central region thereof, with the radially outerperiphery of said skeleton being spaced inwardly from the outerperiphery of said wheel, said skeleton being readily lateral-1y flexibleso as not substantially to impair such normal lateral flexibility ofsaid body in use but being substantially radially rigid efliectively toresist the otherwise normal radial distension of said body due tocentrifugal force developed during use thereof.

11. The combination of claim 10 wherein said reinrforcing skeleton is oflaminated fibrous material.

12. The combination of claim 10 wherein said body is of foamed resin andsaid reinforcing skeleton is of laminated fibrous material.

13. The combination of claim 10 wherein said abrasive is concentrated inan annular outer region of said resin body and said flexible reinforcingskeleton is embedded Within the radially inner, nonabrasive region ofsaid body.

References Cited by the Examiner UNITED STATES PATENTS 507,214 10/1893Chase 51394 1,238,883 9/1917 Burlew 51-394 2,460,367 2/ 1949 Sharpe51298 2,624,660 1/1953 Teague 51300 2,826,016 3/1958 Hurst 51206.62,860,961 11/1958 Gregor et al. 51298 2,862,806 12/ 1958 Nestor 512983,177,056 4/ 1965 Hofelmann et al 51296 15 ROBERT c. RIORDON, PrimaryExaminer.

L. S. SELMAN, Asssitant Examiner.

10. A FINISHING AND POLISHING WHEEL HAVING A RESIN AND ABRASIVE BODYNORMALLY LATERALLY FLEXIBLE UNDER LATERAL PRESSURES ENCOUNTERED IN USEAND RADIALLY DISTENSIBLE UNDER CENTRIFUGAL FORCE AT OPERATING SPEEDSENCOUNTERED IN USE, A FLEXIBLE REINFORCING SKELETON EMBEDDED WITHIN SAIDBODY AND CONCENTRIC THEREWITH, SAID SKETETON EXTENDING RADIALLYOUTWARDLY FROM THE CENTRAL REGION THEREOF, WITH THE RADIALLY OUTERPERIPHERY OF SAID SKELETON BEING SPACED INWARDLY FROM THE OUTERPERIPHERY OF SAID WHEEL, SAID SKELETON BEING READILY LATERALLY FLEXIBLESO AS NOT SUBSTANTIALLY TO IMPAIR SUCH NORMAL LATERAL FLEXIBILITY OFSAID BODY IN USE BUT BEING SUBSTANTIALLY RADIALLY RIGID EFFIECTIVELY TORESIST THE OTHERWISE NORMAL RADIAL DISTENSION OF SAID BODY DUE TOCENTRIFUGAL FORCE DEVELOPED DURING USE THEREOF.